How can I concatenate following strings into simpified patterns:
(1)
from
dir1 dir1:dir2 dir1:dir2:dir3 :dir4:
changed into
dir1:dir2:dir3:dir4
(2)
from
/bin:/usr/bin /usr/bin:/bin /usr/etc:/etc:
changed into
/bin:/usr/bin:/usr/etc:/etc:
(3)
from
dir1:dir3:dir1:dir2:dir3 dir2
changed into
dir1:dir3:dir2

Any comment for help.

Bash one-liner to read your input string and echo the transformed version:

read string ; declare -a a=(${string//:/ }) ; i=0 ; while [[ ${a[$i]} != "" ]] ; do [[ ${str/ ${a[$i]}/} = $str ]] && str=$str" ${a[i]}" ; ((i++)) ; done ; str=${str// /:} ; echo ${str#:} ; unset a i str string

Works okay assuming you didn't want the trailing ':' in (2).